Metal detectors don't (typically) detect body jewelery so I don't think they are very useful in a clinical setting since they'd have to detect that sort of thing.
Source: I have a bunch of body jewelery and been through a bunch of metal detectors and never set any off.
Well yes the ones used in security checkpoints are probably only set to detect big pieces of metal like guns and knives. It's a pain if they go off every time someone walks through with an earring or a metal button or zipper.
But people do use metal detectors to reliably find bottle caps, jewelry, coins, etc, under several inches of sand and soil.
Source: I have a bunch of body jewelery and been through a bunch of metal detectors and never set any off.